Display device, method for driving the same, and electronic apparatus

ABSTRACT

A display device including a pixel array unit having a matrix of pixels each configured such that an anode electrode of an organic electroluminescent element is connected to a source electrode of a drive transistor, a gate electrode of the drive transistor is connected to a source or drain electrode of a writing transistor, and a storage capacitor is connected between the gate and source electrodes of the drive transistor, scanning lines and power supply lines for individual pixel rows, and signal lines for individual pixel columns. A video signal reference potential is supplied to the signal lines for a period during which a scanning signal is supplied to the scanning lines during driving of pixels in a preceding row. During threshold correction for the drive transistor in a current pixel, the video signal reference potential and a potential of the cathode electrode of the organic electroluminescent element are equal.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.15/284,935 filed Oct. 4, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/989,461 filed Jan. 6, 2016, now U.S. Pat. No.9,496,324 issued Nov. 15, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/790,898 filed Jul. 2, 2015, now U.S. Pat. No.9,299,762 issued Mar. 29, 2016, which is a continuation of U.S. patentapplication Ser. No. 13/926,655 filed on Jun. 25, 2013, now U.S. Pat.No. 9,136,285 issued Sep. 15, 2015, which is a continuation of U.S.patent application Ser. No. 12/632,330 filed Dec. 7, 2009, now U.S. Pat.No. 8,570,245 issued on Oct. 29, 2013, the entireties of which areincorporated herein by reference to the extent permitted by law. Thepresent application claims the benefit of priority to Japanese PatentApplications No. JP 2008-315467 filed on Dec. 11, 2008 and JapanesePatent Application No. JP 2008-316551 filed on Dec. 12, 2008 in theJapan Patent Office, the entireties of which are incorporated byreference herein to the extent permitted by law.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a display device, a method for drivingthe same, and an electronic apparatus. More specifically, the presentinvention relates to a planar (flat panel) display device having amatrix of pixels each including an electro-optical element, a method fordriving the display device, and an electronic apparatus.

2. Description of the Related Art

In recent years, in the fields of display devices for displaying images,the prevalence of planar display devices having a matrix of pixels(pixel circuits) each including a light-emitting element has beenrapidly increasing. Planar display devices, for example, organicelectroluminescent (EL) display devices including organic EL elementsthat utilize a phenomenon in which the application of an electric fieldto an organic thin film induces light emission, have been developed andare being commercialized.

Since organic EL elements can be driven with an applied voltage of 10 Vor less, power consumption is low. In addition, due to the self-emittingcharacteristics, organic EL elements do not use a light source(backlight) which is necessary for liquid crystal display devices.Furthermore, due to the response speed as high as about several ofmicroseconds, organic EL elements cause no afterimages during thedisplay of moving images.

As in liquid crystal display devices, organic EL display devices can usesimple (passive) matrix and active matrix driving schemes. In recentyears, the development of active-matrix display devices including pixelcircuits having active elements, for example, insulated gate fieldeffect transistors (in general, thin film transistors (TFTs)), has beengreatly accelerated.

In general, it is common knowledge that the current-voltagecharacteristic (I-V characteristic) of organic EL elements deteriorateswith time (called deterioration over time). Furthermore, a thresholdvoltage Vth of a drive transistor or the mobility μ of a semiconductorthin film forming a channel in the drive transistor (hereinafterreferred to as the “mobility μ of the drive transistor”) changes withtime or differs from pixel to pixel due to the variations in thefabrication process.

Accordingly, in order to maintain the light emission luminance oforganic EL elements at a constant level without suffering from the aboveinfluence, each of the pixel circuits is configured to have a functionfor compensating for characteristic changes in the organic EL elements,and also correction functions for correcting the change in the thresholdvoltage Vth of a drive transistor (hereinafter referred to as a“threshold correction”) and correcting the change in the mobility μ of adrive transistor (hereinafter referred to as “mobility correction”)(see, for example, Japanese Unexamined Patent Application PublicationNo. 2006-133542).

SUMMARY OF THE INVENTION

In the potential setting in a pixel circuit of the related art, however,a short between the gate and cathode of a driving transistor in a pixelcauses non-light emission of a defective pixel. In addition, anotherproblem occurs in that an area where luminance changes (hereinafterreferred to as a “luminance change area”) in several pixels before thetransfer is perceived as a linear defect. In terms of visibility, theprovision of a standard based on the number of non-light emitting pixelsin the display area is not permitted for a change in luminance. Inparticular, for an increase in luminance, even one non-light emittingpixel is not permitted. Particular, if luminance increases in thedisplay area, there is a problem in that a linear defect is perceived.

In a pixel circuit of the related art, furthermore, a storage capacitorand an auxiliary capacitor are arranged adjacent to each other, andwirings connected to those capacitors are provided in the same layer.There is a risk of the wirings in the same layer being shorted to eachother during the fabrication process due to dust or the like thereon. Ashort between the wirings causes a short between the gate of the drivingtransistor and the cathode of the organic EL element, which are broughtinto conduction with the wirings. A short between the gate of the drivetransistor and the cathode of the organic EL element involves problemsin that a defective pixel where the short has occurred is notilluminated and a luminance change area in several pixels preceding inthe transfer direction is perceived as a linear defect. In terms ofvisibility, the provision of a standard based on the number of non-lightemitting pixels in the display area is not permitted for a change inluminance. In particular, for luminance increase, even one non-lightemitting pixel is not permitted. Particular, if luminance increases inthe display area, there is a problem in that a linear defect isperceived.

It is therefore desirable that even if the gate of a driving transistorand a cathode are electrically shorted to each other within a pixel, aluminance change area not be perceived as a linear defect although adefective pixel may not be illuminated.

It is also desirable to prevent an electric short from occurring betweenthe gate electrode of a driving transistor and a cathode electrode sothat due to the short, a non-light emitting pixel and a luminance changearea may not be perceived as linear defects.

An embodiment of the present invention provides a display deviceincluding a pixel array unit having pixels arranged in a matrix, eachpixel having a circuit configuration including an organicelectroluminescent element, a drive transistor, a writing transistor,and a storage capacitor, wherein an anode electrode of the organicelectroluminescent element is connected to a source electrode of thedrive transistor, a gate electrode of the drive transistor is connectedto a source electrode or drain electrode of the writing transistor, andthe storage capacitor is connected between the gate and sourceelectrodes of the drive transistor; scanning lines disposed forindividual rows of the pixels in the pixel array unit and configured tosupply a scanning signal to the gate electrodes of the writingtransistors; power supply lines disposed for the individual rows of thepixels in the pixel array unit and configured to selectively supply afirst potential and a second potential lower than the first potential tothe drain electrodes of the drive transistors; and signal lines disposedfor individual columns of the pixels in the pixel array unit andconfigured to selectively supply a video signal and a video signalreference potential to the drain electrodes or source electrodes of thewriting transistors. The video signal reference potential is supplied tothe signal lines for a period during which the scanning signal issupplied to the scanning lines during driving of pixels in a precedingrow, and when threshold correction for the drive transistor in a currentpixel is performed, the video signal reference potential and a potentialof a cathode electrode of the organic electroluminescent element areequal to each other.

The embodiment of the present invention also provides a method fordriving the display device, for setting the video signal referencepotential and a potential of the cathode electrode of the organicelectroluminescent element so as to have a same potential value.

The embodiment of the present invention also provides an electronicapparatus including the display device described above, which isprovided in a housing of the electronic apparatus.

In the embodiment of the present invention, a video signal referencepotential and a potential of a cathode electrode are set to have a samepotential value, whereby even with the occurrence of an electrical shortbetween the gate electrode of a driving transistor and a cathodeelectrode within a pixel, the reference potentials of pixels in thepreceding pixel row can be made constant.

Another embodiment of the present invention provides a display deviceincluding a pixel array unit having pixels arranged in a matrix, eachpixel having a circuit configuration including an electro-opticalelement, a drive transistor, a writing transistor, a storage capacitor,and an auxiliary capacitor, wherein a first electrode of theelectro-optical element is connected to a source electrode of the drivetransistor, a gate electrode of the drive transistor is connected to asource electrode or drain electrode of the writing transistor, thestorage capacitor is connected between the gate and source electrodes ofthe drive transistor, and the auxiliary capacitor is connected betweenthe first electrode of the electro-optical element and a secondelectrode of the electro-optical element. The storage capacitor and theauxiliary capacitor are arranged adjacent to each other. A wiring of thestorage capacitor, which is brought into conduction with the gateelectrode of the drive transistor, and a wiring of the auxiliarycapacitor, which is brought into conduction with the second electrode ofthe electro-optical element, are provided in different layers.

The embodiment of the present invention also provides an electronicapparatus including the display device described above, which isprovided in a housing of the electronic apparatus.

In the embodiment of the present invention, a wiring of a storagecapacitor, which is brought into conduction with the gate electrode of adrive transistor, and a wiring of an auxiliary capacitor, which isbrought into conduction with a second electrode of an electro-opticalelement, are provided in different layers. This can effectively avoidthe occurrence of a short between the wirings.

An electro-optical element may be an organic EL element having a firstelectrode serving as an anode electrode and a second electrode servingas a cathode electrode. Wirings provided in different layers may beprincipal wirings that are disposed on a flat surface of a substrate anda flat surface of an insulating film on the substrate, and contacts andthe like provided between the layers are not included.

According to an embodiment of the present invention, even if the gateand cathode of a driving transistor are electrically shorted to eachother, a luminance change area can be prevented from being perceived asa linear defect although a defective pixel may not be illuminated.

According to another embodiment of the present invention, the occurrenceof an electrical short between the gate electrode of a drive transistorand a second electrode of an electro-optical element can be effectivelyavoided. Therefore, a luminance change area can be prevented from beingperceived as a linear defect although a defective pixel may not beilluminated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram schematically showing theconfiguration of an active-matrix organic EL display device according toan embodiment of the present invention;

FIG. 2 is a circuit diagram showing a specific example configuration ofa pixel (pixel circuit);

FIG. 3 is a timing waveform diagram illustrating the operation of theactive-matrix organic EL display device according to the embodiment ofthe present invention;

FIGS. 4A to 4D are diagrams (first part) illustrating the circuitoperation of the active-matrix organic EL display device according tothe embodiment of the present invention;

FIGS. 5A to 5D are diagrams (second part) illustrating the circuitoperation of the active-matrix organic EL display device according tothe embodiment of the present invention;

FIGS. 6A to 6C are diagrams (third part) illustrating the circuitoperation of the active-matrix organic EL display device according tothe embodiment of the present invention;

FIGS. 7A and 7B are diagrams illustrating the effect of a short on adrive transistor;

FIG. 8 is a timing waveform diagram when a defect has occurred;

FIGS. 9A and 9B are circuit diagrams illustrating an example of thesetting of a pixel potential according to the present embodiment;

FIG. 10 is a system configuration diagram showing an example of adisplay device according to the present embodiment;

FIG. 11 is a timing waveform diagram illustrating a method for driving adisplay device according to the present embodiment;

FIG. 12 is a timing waveform diagram when a defect has occurred in thepixel configuration according to the present embodiment;

FIG. 13 is a perspective view showing the appearance of a television setaccording to an application example of the present embodiment;

FIGS. 14A and 14B are perspective views showing the appearance of adigital camera according to another application example of the presentembodiment and showing the front and rear of the digital camera,respectively;

FIG. 15 is a perspective view showing the appearance of a notebook-sizedpersonal computer according to another application example of thepresent embodiment;

FIG. 16 is a perspective view showing the appearance of a video cameraaccording to another application example of the present embodiment;

FIGS. 17A to 17G are external views showing a mobile phone according toanother application example of the present embodiment, in which FIGS.17A and 17B are a front view and a side view of the mobile phone whichis in its open state, respectively, and FIGS. 17C, 17D, 17E, 17F, and17G are a front view, a left side view, a right side view, a top view,and a bottom view of the mobile phone which is in its closed state,respectively;

FIGS. 18A to 18C are diagrams illustrating a wiring structure of apixel, in which FIG. 18A is a plan view of the pixel and FIGS. 18B and18C are cross-sectional views taken along the lines XVIIIB-XVIIIB andXVIIIC-XVIIIC of FIG. 18A;

FIGS. 19A to 19C are diagrams (first part) illustrating an examplewiring structure according to the present embodiment; and

FIG. 20 is a diagram (second part) illustrating the example wiringstructure according to the present embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described. Thedescription will be given in the following order:

1. Display Device according to Present Embodiment (System Configuration,Pixel Circuit, and Circuit Operation)

2. Problems Caused by Short between Gate of Drive Transistor and Cathode(Equivalent Circuit and Timing Waveform Diagram)

3. Example Configuration according to Present Embodiment (Pixel Circuit,System Configuration, and Driving Method)

4. Application Examples (Various Examples of Application in ElectronicApparatuses)

5. Example Configuration according to Present Embodiment (Pixel Circuit,System Configuration, Wiring Structure, and Driving Method)

1. Display Device According to Present Embodiment System Configuration

FIG. 1 is a system configuration diagram schematically showing theconfiguration of an active-matrix display device according to thepresent embodiment.

A description will now be given of a current-driven electro-opticalelement whose light emission luminance changes in accordance with acurrent value of a current flowing in the device, for example, anactive-matrix organic EL display device in which an organic EL elementis used as a light-emitting element of a pixel (pixel circuit), by wayof example.

As shown in FIG. 1, an organic EL display device 100 is configured toinclude a pixel array unit 102 having pixels (PXLC) 101 arranged in atwo-dimensional matrix, and a driving unit arranged around the pixelarray unit 102 to drive the pixels 101. The driving unit for driving thepixels 101 includes, for example, a horizontal drive circuit 103, awrite scanning circuit 104, and a power supply scanning circuit 105.

The pixel array unit 102 has scanning lines WSL-1 to WSL-m, power supplylines DSL-1 to DSL-m, and signal lines DTL-1 to DTL-n for the m-rown-column pixel array. The scanning lines WSL-1 to WSL-m and the powersupply lines DSL-1 to DSL-m are disposed for the individual rows, andthe signal lines DTL-1 to DTL-n are disposed for the individual pixelcolumns.

The pixel array unit 102 is typically defined on a transparentinsulating substrate such as a glass substrate, and has a planar (flat)panel structure. Each of the pixels 101 in the pixel array unit 102 canbe formed using an amorphous silicon thin film transistor (TFT) or alow-temperature polysilicon TFT. In a case where low-temperaturepolysilicon TFTs are used, the horizontal drive circuit 103, the writescanning circuit 104, and the power supply scanning circuit 105 can alsobe mounted on the display panel (substrate) on which the pixel arrayunit 102 is defined.

The write scanning circuit 104 may be formed of a shift register forsequentially shifting (transferring) a start pulse sp in synchronizationwith a clock pulse ck, or any other suitable device. In order to write avideo signal in the pixels 101 in the pixel array unit 102, the writescanning circuit 104 sequentially supplies write pulses (scanningsignals) WS1 to WSm to the scanning lines WSL-1 to WSL-m. Accordingly,the pixels 101 in the pixel array unit 102 are scanned in row-by-roworder (line sequentially scanned).

The power supply scanning circuit 105 may be formed of a shift registerfor sequentially shifting the start pulse sp in synchronization with theclock pulse ck, or any other suitable device. In synchronization withline sequentially scanning performed by the write scanning circuit 104,the power supply scanning circuit 105 selectively supplies power supplyline potentials DS1 to DSm, which are switched between a first potentialVcc_H and a second potential Vcc_L lower than the first potential Vcc_H,to the power supply lines DSL-1 to DSL-m. Accordingly, lightemission/non-light emission of the pixels 101 can be controlled.

The horizontal drive circuit 103 appropriately selects one of a signalvoltage Vsig of a video signal corresponding to luminance information,which is supplied from a signal supply source (not shown) (hereinafteralso referred to simply as a “signal voltage”), and a signal linereference potential Vo, and writes the selected one in the pixels 101 inthe pixel array unit 102 via the signal lines DTL-1 to DTL-n, forexample, on a row-by-row basis. In other words, the horizontal drivecircuit 103 adopts a line sequential write drive mode in which a signalvoltage Vin of a video signal is written row by row (line by line).

The signal line reference potential Vo is a voltage (for example, avoltage corresponding to black level) which the signal voltage Vin ofthe video signal is based on. Further, the second potential Vcc_L is setto a potential lower than the signal line reference potential Vo, forexample, a potential lower than a potential Vo−Vth where Vth denotes thethreshold voltage of a drive transistor, preferably, a potentialsufficiently lower than the potential Vo−Vth.

Pixel Circuit

FIG. 2 is a circuit diagram showing a specific example configuration ofeach of the pixels (pixel circuits) 101.

As shown in FIG. 2, the pixel 101 has a current-driven electro-opticalelement whose light emission luminance changes in accordance with acurrent value of a current flowing in the device, for example, anorganic EL element 1D, as a light-emitting element. The pixel 101 has apixel configuration including, in addition to the organic EL element 1D,a drive transistor 1B, a writing transistor 1A, and a storage capacitor1C, that is, a 2Tr/1C pixel configuration having two transistors (Tr)and one capacitor (C).

In the pixel 101 having the above configuration, each of the drivetransistor 1B and the writing transistor 1A is implemented using anN-channel TFT. However, the conductor combination of transistors usedherein, namely, the drive transistor 1B and the writing transistor 1A,is merely an example, and any other combination of transistors may beemployed.

The organic EL element 1D has a cathode electrode connected to a commonpower supply line 1H that is commonly disposed for all the pixels 101.The drive transistor 1B has a source electrode connected to an anodeelectrode of the organic EL element 1D, and a drain electrode connectedto the power supply line DSL (DSL-1 to DSL-m).

The writing transistor 1A has a gate electrode connected to the scanningline WSL (WSL-1 to WSL-m), one electrode (source electrode or drainelectrode) connected to the signal line DTL (DTL-1 to DTL-n), and theother electrode (drain electrode or source electrode) connected to agate electrode of the drive transistor 1B.

The storage capacitor 1C has one electrode connected to the gateelectrode of the drive transistor 1B, and the other electrode connectedto the source electrode of the drive transistor 1B (the anode electrodeof the organic EL element 1D).

In the pixel 101 having a 2Tr/1C pixel configuration, the writingtransistor 1A is brought into a conducting state in response to ascanning signal WS applied to the gate electrode from the write scanningcircuit 104 via the scanning line WSL. Thus, the signal voltage Vin ofthe video signal corresponding to the luminance information, which issupplied from the horizontal drive circuit 103 via the signal line DTL,or the signal line reference potential Vo is sampled and written in thepixel 101.

The written signal voltage Vin or signal line reference potential Vo isapplied to the gate electrode of the drive transistor 1B and is alsostored in the storage capacitor 1C. When the potential DS of the powersupply line DSL (DSL-1 to DSL-m) is set to the first potential Vcc_H,the drive transistor 1B is supplied with a current from the power supplyline DSL and supplies a driving current of the current valuecorresponding to the voltage value of the signal voltage Vin stored inthe storage capacitor 1C to the organic EL element 1D to drive theorganic EL element 1D to emit light.

Circuit Operation of Organic EL Display Device

Next, the circuit operation of the organic EL display device 100 havingthe above configuration will be described with reference to a timingwaveform diagram shown in FIG. 3 and operation-explaining diagrams shownin FIG. 4A to FIG. 6C. In the operation-explaining diagrams shown inFIGS. 4A to 6C, for simplicity of illustration, the writing transistor1A is represented by the symbol of switch. Since the organic EL element1D has a capacitive component, an EL capacitor 1I is also illustrated.

The timing waveform diagram shown in FIG. 3 illustrates changes in thepotential (write pulse) WS of the scanning line WSL (WSL-1 to WSL-m),changes in the potential DS (Vcc_H or Vcc_L) of the power supply lineDSL (DSL-1 to DSL-m), and changes in gate potential Vg and sourcepotential Vs of the drive transistor 1B.

(Light-Emission Period)

In the timing waveform diagram shown in FIG. 3, the organic EL element1D is in a light emitting state prior to time t1 (light-emissionperiod). In the light-emission period, the potential DS of the powersupply line DSL is set to the first potential Vcc_H and the writingtransistor 1A is in a non-conducting state.

During this period, the drive transistor 1B is set so as to operate inthe saturation region. Thus, as shown in FIG. 4A, a driving current(drain-source current) Ids corresponding to a gate-source voltage Vgs ofthe drive transistor 1B is supplied to the organic EL element 1D fromthe power supply line DSL through the drive transistor 1B. Therefore,the organic EL element 1D emits light with a luminance corresponding tothe current value of the driving current Ids.

(Threshold Correction Preparation Period)

A new field of line sequentially scanning begins at time t1. As shown inFIG. 4B, the potential DS of the power supply line DSL is switched fromthe first potential (hereinafter referred to as a “high potential”)Vcc_H to the second potential (hereinafter referred to as a “lowpotential”) Vcc_L sufficiently lower than the signal line referencepotential Vo−Vth of the signal line DTL.

Here, the organic EL element 1D has a threshold voltage Vel and thecommon power supply line 1H has a potential Vcath. If the low potentialVcc_L satisfies condition Vcc_L<Vel+Vcath, then, the source potential Vsof the drive transistor 1B is substantially equal to the low potentialVcc_L. Thus, the organic EL element 1D enters the reverse biased stateand light is extinguished.

Then, at time t2, a transition of the potential WS of the scanning lineWSL from the low-potential side to the high-potential side brings thewriting transistor 1A into the conducting state, as shown in FIG. 4C. Atthis time, since the signal line reference potential Vo is supplied fromthe horizontal drive circuit 103 to the signal line DTL, the gatepotential Vg of the drive transistor 1B is set to the signal linereference potential Vo. Further, the source potential Vs of the drivetransistor 1B is set to the potential Vcc_L, which is sufficiently lowerthan the signal line reference potential Vo.

At this time, the gate-source voltage Vgs of the drive transistor 1B isset to a potential Vo−Vcc_L. Here, it is necessary to establishpotential relationship Vo−Vcc_L>Vth because the threshold correctionoperation described below is not performed unless the potential Vo−Vcc_Lis greater than the threshold voltage Vth of the drive transistor 1B.Accordingly, an operation of performing initialization with the gatepotential Vg of the drive transistor 1B fixed (set) to the signal linereference potential Vo and the source potential Vs to the low potentialVcc_L is an operation for preparing threshold correction.

(First Threshold Correction Period)

Then, at time t3, as shown in FIG. 4D, the potential DS of the powersupply line DSL is switched from the low potential Vcc_L to the highpotential Vcc_H. Then, the source potential Vs of the drive transistor1B starts to increase, and a first threshold correction period begins.The increase in the source potential Vs of the drive transistor 1Bduring the first threshold correction period allows the gate-sourcevoltage Vgs of the drive transistor 1B to have a predetermined potentialVx1. The potential Vx1 is stored in the storage capacitor 1C.

Subsequently, at time t4 with which the second half of this horizontalperiod (1H) begins, as shown in FIG. 5A, the signal voltage Vin of thevideo signal is supplied from the horizontal drive circuit 103 to thesignal line DTL, thus causing a transition of the potential of thesignal line DTL from the signal line reference potential Vo to thesignal voltage Vin. During this period, the signal voltage Vin iswritten in pixels in another row.

At this time, in order to prevent the signal voltage Vin from beingwritten in pixels in the current row, a transition of the potential WSof the scanning line WSL from the high-potential side to thelow-potential side brings the writing transistor 1A into thenon-conducting state. Thus, the gate electrode of the drive transistor1B is separated from the signal line DTL and becomes floating.

When the gate electrode of the drive transistor 1B is floating, becauseof the storage capacitor 1C connected between the gate and the source ofthe drive transistor 1B, if the source potential Vs of the drivetransistor 1B changes, the gate potential Vg of the drive transistor 1Balso changes in accordance with (or following) the change in the sourcepotential Vs. This is called a bootstrap operation based on the storagecapacitor 1C.

Even after time t4, the source potential Vs of the drive transistor 1Bcontinues increasing and finally increases by Va1 (Vs=Vo−Vx1+Va1). Atthis time, due to the bootstrap operation, the gate potential Vg of thedrive transistor 1B also increases by Va1 (Vg=Vo+Va1) in accordance withthe increase in the source potential Vs.

(Second Threshold Correction Period)

At time t5, the next horizontal period begins, and, as shown in FIG. 5B,a transition of the potential WS of the scanning line WSL from thelow-potential side to the high-potential side brings the writingtransistor 1A into the conducting state. At the same time, the signalline reference potential Vo instead of the signal voltage Vin issupplied from the horizontal drive circuit 103 to the signal line DTL,and a second threshold correction period begins.

During the second threshold correction period, since the writingtransistor 1A is brought into the conducting state, the signal linereference potential Vo is written. Thus, the gate potential Vg of thedrive transistor 1B is initialized again to the signal line referencepotential Vo. At this time, in accordance with the drop of the gatepotential Vg, the source potential Vs also decreases. Then, the sourcepotential Vs of the drive transistor 1B again starts to increase.

Then, the increase in the source potential Vs of the drive transistor 1Bduring the second threshold correction period allows the gate-sourcevoltage Vgs of the drive transistor 1B to have a predetermined potentialVx2. The potential Vx2 is stored in the storage capacitor 1C.

Subsequently, at time t6 with which the second half of this horizontalperiod (1H) begins, as shown in FIG. 5C, the signal voltage Vin of thevideo signal is supplied from the horizontal drive circuit 103 to thesignal line DTL, thus causing a transition of the potential of thesignal line DTL from the offset voltage Vo to the signal voltage Vin.During this period, the signal voltage Vin is written in pixels inanother row (row subsequent to the row where the previous writing hasbeen performed).

At this time, in order to prevent the signal voltage Vin in pixels frombeing written in the current row, a transition of the potential WS ofthe scanning line WSL from the high-potential side to the low-potentialside brings the writing transistor 1A into the non-conducting state.Thus, the gate electrode of the drive transistor 1B is separated fromthe signal line DTL and becomes floating.

Even after time t6, the source potential Vs of the drive transistor 1Bcontinues increasing and finally increases by Va2 (Vs=Vo−Vx1+Va2). Atthis time, due to the bootstrap operation, the gate potential Vg of thedrive transistor 1B also increases by Va2 (Vg=Vo+Va2) in accordance withthe increase in the source potential Vs.

(Third Threshold Correction Period)

At time t7, the next horizontal period begins, and, as shown in FIG. 5D,a transition of the potential WS of the scanning line WSL from thelow-potential side to the high-potential side brings the writingtransistor 1A into the conducting state. At the same time, the signalline reference potential Vo instead of the signal voltage Vin issupplied from the horizontal drive circuit 103 to the signal line DTL,and a third threshold correction period begins.

During the third threshold correction period, since the writingtransistor 1A is brought into the conducting state, the signal linereference potential Vo is written. Thus, the gate potential Vg of thedrive transistor 1B is initialized again to the signal line referencepotential Vo. At this time, in accordance with the drop of the gatepotential Vg, the source potential Vs also decreases. Then, the sourcepotential Vs of the drive transistor 1B again starts to increase.

The increase in the source potential Vs of the drive transistor 1Ballows the gate-source voltage Vgs of the drive transistor 1B toconverge to the threshold voltage Vth of the drive transistor 1B. Thus,the voltage corresponding to the threshold voltage Vth is stored in thestorage capacitor 1C.

The threshold correction operation performed three times as describedabove allows the detection of the threshold voltage Vth of the drivetransistor 1B of each of the pixel and the storage of the voltagecorresponding to the threshold voltage Vth in the storage capacitor 1C.In order to prevent a current from flowing in the organic EL element 1Dwhile causing a current to flow in the storage capacitor 1C during thethree threshold correction periods, the potential Vcath of the commonpower supply line 1H is set so that the organic EL element 1D can berendered into a cut-off state.

(Signal Writing Period & Mobility Correction Period)

Then, at time t8, a transition of the potential WS of the scanning lineWSL to the low-potential side brings the writing transistor 1A into thenon-conducting state, as shown in FIG. 6A. At the same time, thepotential of the signal line DTL is switched from the offset voltage Voto the signal voltage Vin of the video signal.

Since the writing transistor 1A is brought into the non-conductingstate, the gate electrode of the drive transistor 1B becomes floating.However, the gate-source voltage Vgs is equal to the threshold voltageVth of the drive transistor 1B and therefore the drive transistor 1B isrendered into a cut-off state. Thus, the drain-source current Ids doesnot flow in the drive transistor 1B.

Subsequently, at time t9, a transition of the potential WS of thescanning line WSL to the high-potential side brings the writingtransistor 1A into the conducting state, as shown in FIG. 6B. Thus, thesignal voltage Vin of the video signal is sampled and written in thepixel 101. The writing of the signal voltage Vin by the writingtransistor 1A allows the gate potential Vg of the drive transistor 1B toincrease by the signal voltage Vin.

Then, when the drive transistor 1B is driven by the signal voltage Vinof the video signal, the threshold voltage Vth of the drive transistor1B is canceled out with the voltage corresponding to the thresholdvoltage Vth stored in the storage capacitor 1C, thereby performingthreshold correction. A principle of threshold correction will bedescribed below.

At this time, since the organic EL element 1D is initially in thecut-off state (high-impedance state), the current (drain-source currentIds), which flows in the drive transistor 1B from the power supply lineDSL in accordance with the signal voltage Vin of the video signal, flowsin the EL capacitor 1I of the organic EL element 1D. Therefore, thecharging of the EL capacitor 1I is started.

Due to the charging of the EL capacitor 1I, the source potential Vs ofthe drive transistor 1B increases with time. Since the variation of thethreshold voltage Vth of the drive transistor 1B has already beencorrected (threshold correction) at this time, the drain-source currentIds in the drive transistor 1B depends on the mobility μ of the drivetransistor 1B.

Afterwards, when the source potential Vs of the drive transistor 1Bincreases up to a potential Vo−Vth+ΔV, the gate-source voltage Vgs ofthe drive transistor 1B is given by Vin+Vth−ΔV. That is, the amount ofincrease of the source potential Vs, ΔV, is subtracted from the voltagestored in the storage capacitor 1C (Vin+Vth−ΔV), in other words, thecharge in the storage capacitor 1C is discharged. Thus, a negativefeedback is applied. The amount of increase ΔV of the source potentialVs therefore represents the amount of negative feedback.

Accordingly, the drain-source current Ids flowing in the drivetransistor 1B is input to the gate of the drive transistor 1B, that is,the drain-source current Ids is negatively fed back to the gate-sourcevoltage Vgs, thereby canceling the dependency of the drain-sourcecurrent Ids of the drive transistor 1B upon the mobility μ. That is,mobility correction for correcting the variation in the mobility μ foreach pixel is performed.

More specifically, the higher the signal voltage Vin of the videosignal, the greater the drain-source current Ids and therefore thelarger the absolute value of the amount of negative feedback (amount ofcorrection) ΔV. Accordingly, mobility correction can be performed inaccordance with the light emission luminance level. When the signalvoltage Vin of the video signal is kept constant, the higher themobility μ of the drive transistor 1B, the larger the absolute value ofthe amount of negative feedback ΔV. Thus, the variation of the mobilityμ for each pixel can be removed. A principle of mobility correction willbe described below.

(Light-Emission Period)

Then, at time t10, a transition of the potential WS of the scanning lineWSL to the low-potential side brings the writing transistor 1A into thenon-conducting state, as shown in FIG. 6C. Thus, the gate electrode ofthe drive transistor 1B is separated from the signal line DTL andbecomes floating.

The gate electrode of the drive transistor 1B becomes floating and, atthe same time, the drain-source current Ids in the drive transistor 1Bstarts to flow in the organic EL element 1D. Thus, the anode potentialof the organic EL element 1D increases in accordance with thedrain-source current Ids in the drive transistor 1B.

The increase in the anode potential of the organic EL element 1D isequivalent to the increase in the source potential Vs of the drivetransistor 1B. As the source potential Vs of the drive transistor 1Bincreases, the gate potential Vg of the drive transistor 1B alsoincreases in accordance therewith due to the bootstrap operation of thestorage capacitor 1C.

At this time, if it is assumed that the bootstrap gain is 1 (idealvalue), the amount of increase in the gate potential Vg is equal to theamount of increase in the source potential Vs. Therefore, thegate-source voltage Vgs of the drive transistor 1B during thelight-emission period is kept at a constant value given by Vin+Vth−ΔV.Then, at time t11, the potential of the signal line DTL is switched fromthe signal voltage Vin of the video signal to the signal line referencepotential Vo.

As can be understood from the operations described above, in the presentexample, threshold correction periods are provided over a total of 3Hperiods, that is, a 1H period during which signal writing and mobilitycorrection are performed and 2H periods preceding the 1H period. Thus, asufficient period of time can be ensured as threshold correctionperiods. This ensures that the threshold voltage Vth of the drivetransistor 1B can be detected and stored in the storage capacitor 1C,and also ensures that the threshold correction operation can reliably beperformed.

While threshold correction periods are provided over 3H periods, this ismerely an example. If a sufficient length of threshold correction periodcan be ensured within a 1H period during which signal writing andmobility correction are performed, it is not necessary to set athreshold correction period over preceding horizontal periods.Conversely, if the length of 1H period is short due to the improveddefinition and even if threshold correction periods provided over 3Hperiods are not sufficient, threshold correction periods can be set over4H periods or more.

2. Problems Caused by Short between Gate of Drive Transistor and Cathode

Equivalent Circuit

FIG. 7A shows an equivalent circuit of the pixel circuit shown in FIG. 2in which the gate g of the drive transistor 1B and the cathode 1H areelectrically shorted to each other. At this operation timing, by way ofexample, as shown in FIGS. 4D, 5B, and 5D, the video signal referencepotential Vo is written.

In this manner, an electrical short between the gate g of the drivetransistor 1B and the cathode 1H wired so as to have a low impedancecauses conduction between the video signal line DTL, the gate g of thedrive transistor 1B, and a cathode 1H when the writing transistor 1A isturned on. Therefore, the video signal reference potential Vo suppliedto the video signal lines DTL is drawn to the cathode potential Vcath.

FIG. 7B is a schematic diagram showing a display state where the defectshown in FIG. 7A has occurred. A defective pixel, that is, a pixel inwhich, as shown in FIG. 7A, the gate g of the drive transistor 1B andthe cathode 1H are electrically shorted to each other, is notilluminated. Further, several pixels preceding in the transfer directionform a luminance change area. The luminance change area depends on thetransfer direction, and occurs on the side preceding in the transferdirection all the time.

Timing Waveform Diagram

FIG. 8 is a timing waveform diagram when the defect shown in FIG. 7A hasoccurred. Further, in FIG. 7A, the relationship Vo>Vcath holds by way ofexample. In the timing waveform diagram shown in FIG. 8, the timings ofthe scanning lines having scanning line numbers are represented inassociation with pixels Vn−6 to Vn+2, and the pixel Vn is a defectivepixel. Changes in video signal potential are represented using DTL. InFIG. 8, each of periods (A) to (L) corresponds to one horizontal period(1H).

As shown in FIG. 7A, if the gate g of the drive transistor 1B and thecathode 1H are electrically shorted to each other, a problem occurs inthe periods (F) to (J) shown in FIG. 8. Within those periods, at thetime of a transition of the scanning line WSL corresponding to thedefective pixel Vn to the high-potential side, the potential supplied tothe video signal line DTL is drawn to the cathode potential Vcath.

Consequently, in each of the pixels Vn−4 to Vn−1, the video signalreference potential Vo immediately before the sampling of the videosignal potential is drawn to the cathode potential Vcath. Thus, theinput signal to the gate g of the drive transistor 1B has an amplitudegiven by Vin′=Vsig−Vcath instead of Vin=Vsig−Vo.

In FIG. 8, since Vo>Vcath holds, a signal with a higher amplitude isequivalently written in each of the pixels Vn−4 to Vn−1 than that basedon the video signal reference potential Vo. This leads to increasedluminance levels in the pixels Vn−4 to Vn−1. Consequently, luminanceincreases in several pixels preceding the defective pixel, which isperceived as a linear luminance increasing area. In the defective pixelVn, the video signal potential Vsig is also drawn to the cathodepotential Vcath, resulting in no light emission therefrom.

3. Example Configuration according to Present Embodiment Pixel Circuit

FIG. 9A is a circuit diagram illustrating an example of the setting of apixel potential according to the present embodiment. The pixel circuitincludes an organic EL element 1D, a drive transistor 1B, a writingtransistor 1A, and a storage capacitor 1C.

Specifically, an anode electrode of the organic EL element 1D isconnected to a source electrode of the drive transistor 1B, and a gateelectrode of the drive transistor 1B is connected to a source electrodeor drain electrode of the writing transistor 1A. The storage capacitor1C is further connected between the gate and source electrodes of thedrive transistor 1B.

The signal line DTL is connected to the drain electrode or sourceelectrode of the writing transistor 1A. A gate electrode of the writingtransistor 1A is connected to a scanning line (not shown), and is givena predetermined timing. A power supply line DSL is connected to thedrain electrode of the drive transistor 1B.

In the above configuration of the pixel circuit, in the presentembodiment, the video signal reference potential Vo applied to thesignal line DTL and the potential (cathode potential) Vcath of a cathodeelectrode of the organic EL element 1D have a same potential, namely, apotential Va. Thus, the video signal reference potential Vo is not drawnto a potential higher or lower than the potential Va even within theperiods (F) to (J) shown in FIG. 8. This can prevent a luminance changearea from occurring across the preceding pixels.

Note that the video signal reference potential Vo and the cathodepotential Vcath not be set to desired values with respect to the otherdriving potentials, and satisfy the driving conditions such as thresholdcorrection operations shown in FIG. 3. In order to set the video signalreference potential Vo and the cathode potential Vcath to the samepotential value, in addition to adjusting the video signal referencepotential Vo so as to be equal to the cathode potential Vcath, thecathode potential Vcath may also be adjusted so as to be equal to thevideo signal reference potential Vo. Alternatively, the video signalreference potential Vo and the cathode potential Vcath may be adjustedso as to be equal to any other constant potential. Preferably, thepotential Va is set to the existing setting potential Vo or Vcath,thereby satisfying the driving conditions shown in FIG. 3.

System Configuration

FIG. 10 is a system configuration diagram showing an example of thepresent embodiment. As shown in FIG. 10, an organic EL display device100 is configured to include a pixel array unit 102 having pixels (PXLC)101 arranged in a two-dimensional matrix, and a driving unit arrangedaround the pixel array unit 102 to drive the pixels 101. The drivingunit for driving the pixels 101 includes, for example, a horizontaldrive circuit 103, a write scanning circuit 104, and a power supplyscanning circuit 105.

The pixel array unit 102 has scanning lines WSL-1 to WSL-m, power supplylines DSL-1 to DSL-m, and signal lines DTL-1 to DTL-n for the m-rown-column pixel array. The scanning lines WSL-1 to WSL-m and the powersupply lines DSL-1 to DSL-m are disposed for the individual rows, andthe signal lines DTL-1 to DTL-n are disposed for the individual pixelcolumns. The above configuration is the same as the system configurationshown in FIG. 1.

In the present embodiment, a video signal reference potential Vo appliedto the pixels 101 from the signal lines DTL-1 to DTL-n and the potentialof the cathode electrode (cathode potential) of the organic EL elementin each of the pixels 101 are set to the same potential, Va.

The cathode potential is supplied as a common potential to the organicEL elements of the individual pixels 101. Thus, the potential Va issupplied to a common wiring COM which is brought into conduction withthe cathode electrodes of the organic EL elements in the individualpixels 101.

The video signal reference potential Vo supplied from the signal linesDTL-1 to DTL-n is also set to the potential Va. The horizontal drivecircuit 103 selectively supplies a signal potential Vin and the videosignal reference potential Vo to the signal lines DTL-1 to DTL-n. Thus,the horizontal drive circuit 103 performs control so as to supply thepotential Va when selecting the video signal reference potential Vo.

Thus, a video signal reference potential is supplied to a signal linefor a period during which a scanning signal is supplied to a scanningline during the driving of the preceding pixel row, thus preventing thevideo signal reference potential from being drawn to a potential higheror lower than the potential Va for a period during which thresholdcorrection is performed on a drive transistor in the current pixel. Thatis, even when a gate of a drive transistor and a cathode of an organicEL element are electrically shorted to each other, a luminance changearea can be prevented from occurring across the preceding pixels.

Driving Method

FIG. 11 is a timing waveform diagram illustrating a method for driving adisplay device according to the present embodiment. The timing waveformdiagram shown in FIG. 11 is similar to the timing waveform diagram shownin FIG. 3 in that a light-emission period, threshold correction periods,and a sampling period & mobility correction period are repeated, but isdifferent in that a video signal reference potential supplied to asignal line is set to the potential Va, which is the same as the cathodepotential.

The video signal line potential (DTL) is selectively switched betweenthe video signal Vin and the video signal reference potential Va. Thevideo signal reference potential is set to the potential Va, therebysetting the gate potential (Vg) of the drive transistor to the potentialVa within the threshold correction periods. Since all the pixels arebased on the same potential Va, uniformity in luminance can bemaintained.

FIG. 12 is a timing waveform diagram when a defect has been caused inthe pixel configuration shown in FIG. 9A according to the presentembodiment due to an electrical short between the gate g of the drivetransistor 1B and the cathode 1H. In the timing waveform diagram shownin FIG. 12, the timings of the scanning lines having scanning linenumbers are represented in association with pixels Vn−6 to Vn+2, and thepixel Vn is a defective pixel. Changes in video signal potential arerepresented using DTL. In FIG. 12, each of periods (A) to (L)corresponds to one horizontal period (1H).

As shown in FIG. 9A, if the gate g of the drive transistor 1B and thecathode 1H are electrically shorted to each other, an existingconfiguration may cause a problem in the periods (F) to (J) shown inFIG. 12. That is, within those periods, at the time of a transition ofthe scanning line WSL corresponding to the defective pixel Vn to thehigh-potential side, the potential supplied to the video signal line DTLis drawn to the cathode potential Vcath (see portions indicated bybroken lines shown in FIG. 12).

In the configuration of the present embodiment, in contrast, the videosignal reference potential Vo applied to the video signal line DTL isequal to the potential Va, and the cathode potential Vcath is equal tothe potential Va. That is, control is performed so that the video signalreference potential Vo and the cathode potential Vcath are set to thesame potential Va.

Consequently, in each of the pixels Vn−4 to Vn−1, the video signalreference potential Vo immediately before the sampling of the videosignal potential is equal to the potential Va, thus providing the samecriterion as that of the other pixels. Thus, the input signal to thegate g of the drive transistor 1B has an amplitude given by Vin=Vsig−Va,resulting in no increase in luminance of several pixels preceding thedefective pixel Vn.

In the embodiment described above, the application to an organic ELdisplay device including organic EL elements as electro-optical elementsof the pixels 101 has been described by way of example. However,embodiments of the present invention are not limited to this applicationexample, and can be applied to any display device including acurrent-driven electro-optical element (light-emitting element) whoselight emission luminance changes in accordance with the current value ofa current flowing in the device.

Furthermore, the pixels 101 each having a 2Tr/1C pixel configurationincluding two transistors (Tr) and one capacitor (C) by way of example.However, embodiments of the present invention are not limited thereto,and can also be applied to any other pixel configuration such as a4Tr/1C pixel configuration including four transistors (Tr) and onecapacitor (C).

4. Application Examples

The display device according to the present embodiment described abovecan be applied in various electronic apparatuses shown in FIGS. 13 to17G, by way of example. The display device can be applied to displaydevices used in electronic apparatuses in any field that is configuredsuch that a video signal input to an electronic apparatus or a videosignal generated in an electronic apparatus can be displayed as an imageor video, such as a digital camera, a notebook-sized personal computer,a mobile terminal device such as a mobile phone, and a video camera.

The use of the display device according to the present embodiment as adisplay device in electronic apparatuses in any field provides improvedquality of a displayed image. Therefore, advantageously, variouselectronic apparatuses allow the high-quality display of images.

The display device according to the present embodiment may also includea module having a sealed configuration. For example, a display modulemay be formed so as to be attached to a transparent facing portion ofglass or the like that faces the pixel array unit 102. The transparentfacing portion may have a color filter, a protective film, and the like,and may also have a light shielding film. The display module may have acircuit unit configured to input or output a signal or the like to apixel array unit from the outside, a flexible printed circuit (FPC), andthe like.

Specific examples of electronic apparatuses in which the display deviceof the present embodiment can be applied will be described.

FIG. 13 is a perspective view showing the appearance of a television setaccording to an application example of the present embodiment. Thetelevision set according to the application example includes a videodisplay screen unit 107 having a front panel 108, a glass filter 109,and the like. The video display screen unit 107 can be implemented byusing the display device according to the present embodiment.

FIGS. 14A and 14B are perspective views showing the appearance of adigital camera according to another application example of the presentembodiment and showing the front and rear of the digital camera,respectively. The digital camera according to the present applicationexample includes a light emitting unit 111 for emitting flash light, adisplay unit 112, a menu switch 113, and a shutter button 114. Thedisplay unit 112 can be implemented by using the display deviceaccording to the present embodiment.

FIG. 15 is a perspective view showing the appearance of a notebook-sizedpersonal computer according to an application example of the presentembodiment. The notebook-sized personal computer according to thepresent application example has a main body 121 including a keyboard 122which is operated to enter characters or the like, and a display unit123 for displaying an image. The display unit 123 can be implemented byusing the display device according to the present embodiment.

FIG. 16 is a perspective view showing the appearance of a video cameraaccording to an application example of the present embodiment. The videocamera according to the present application example includes a main unit131, a lens 132 disposed on a side surface of the video camera so as tobe directed toward the front and configured to photograph a subject, astart/stop switch 133 which is operated for photographing, and a displayunit 134. The display unit 134 can be implemented by using the displaydevice according to the present embodiment.

FIGS. 17A to 17G are external views showing a mobile terminal deviceaccording to an application example of the present embodiment, forexample, a mobile phone. FIGS. 17A and 17B are a front view and a sideview of the mobile phone which is in its open state, respectively. FIGS.17C, 17D, 17E, 17F, and 17G are a front view, a left side view, a rightside view, a top view, and a bottom view of the mobile phone which is inits closed state, respectively. The mobile phone according to thepresent application example includes an upper housing 141, a lowerhousing 142, a connection portion (here, a hinge portion) 143, a display144, a sub-display 145, a picture light 146, and a camera 147. Thedisplay 144 or the sub-display 145 can be implemented by using thedisplay device according to the present embodiment.

A description will now be given of other features of the embodiment ofthe present invention for avoiding an electrical short between a gateelectrode of a drive transistor and a second electrode of anelectro-optical element.

FIGS. 18A to 18C are diagrams illustrating a wiring structure of apixel. FIG. 18A is a plan view of the pixel, and FIGS. 18B and 18C arecross-sectional views taken along the lines XVIIIB-XVIIIB andXVIIIC-XVIIIC of FIG. 18A. As in a pattern layout shown in FIG. 18A, astorage capacitor 1C and an auxiliary capacitor 1J are generallyarranged so that, in terms of the area occupied thereby and patternlayout efficiency, at least one side of the storage capacitor 1C and atleast one side of the auxiliary capacitor 1J are adjacent to each other.

As shown in the cross-sectional view of FIG. 18B, the storage capacitor1C and the auxiliary capacitor 1J are arranged so that first electrodesD1 are adjacent to each other on a glass substrate and second electrodesare integrally formed into a polysilicon electrode p-Si with a gateinsulating film M1 between the first electrodes D1 and the secondelectrodes. When a polysilicon electrode p-Si is formed using alow-temperature polysilicon process, the storage capacitor 1C and theauxiliary capacitor 1J are formed of parallel flat plates in such amanner that the first electrodes D1 are formed as first metal wiringsand the second electrodes are formed as a polysilicon electrode p-Si.

In FIG. 18C, in order to illustrate the relationship shown in FIG. 18Bbetween the wiring layout and the upper and lower electrodes serving asthe storage capacitor 1C and the auxiliary capacitor 1J shown in FIG.7A, the numbers in the parentheses in FIG. 18C represent the referencenumerals of the electrodes shown in FIG. 7A. The first metal wiringserving as the first electrode D1(g) of the storage capacitor 1C isconnected to the gate g of the drive transistor 1B, and the polysiliconelectrode p-Si(s) serving as the second electrode is connected to thesource s of the drive transistor 1B. Further, the first metal wiringserving as the first electrode D1(1H) of the auxiliary capacitor 1J isconnected to the cathode 1H of the organic EL element 1D, and thepolysilicon electrode p-Si(s) serving as the second electrode isconnected to the source s of the drive transistor 1B.

In the low-temperature polysilicon process, however, since it isdifficult to perfectly avoid the occurrence of pattern defects due todust or the like generated during the manufacturing process, laserrepair techniques in the TFT manufacturing process are also employed. Inparticular, a short due to a pattern defect in wirings in the same layeroccurs at a significantly higher rate than that of a short in interlayerwirings.

That is, in FIGS. 18A to 18C, the first electrodes D1 of the storagecapacitor 1C and the auxiliary capacitor 1J are provided adjacent toeach other in the same layer (first metal wirings). Thus, dust or thelike is likely to be attached to wirings in the manufacturing process,resulting in a risk of a short occurring therebetween. The short betweenthe wirings corresponds to a short shown in FIG. 7A between the gate gof the drive transistor 1B and the cathode of the organic EL element 1D(the source s of the drive transistor 1B), and may cause a change in theluminance of a defective pixel and pixels preceding in the transferdirection.

5. Example Configuration According to Present Embodiment Pixel Circuit

FIG. 9B is a circuit diagram illustrating the setting of a pixelpotential. The pixel circuit includes an organic EL element 1D, a drivetransistor 1B, a writing transistor 1A, and a storage capacitor 1C.

Specifically, an anode electrode of the organic EL element 1D isconnected to a source electrode of the drive transistor 1B, and a gateelectrode of the drive transistor 1B is connected to a source electrodeor drain electrode of the writing transistor 1A. The storage capacitor1C is further connected between the gate and source electrodes of thedrive transistor 1B. In addition, an auxiliary capacitor 1J is connectedbetween the anode (first electrode) and cathode (second electrode) ofthe organic EL element 1D.

The signal line DTL is connected to the drain electrode or sourceelectrode of the writing transistor 1A. A gate electrode of the writingtransistor 1A is connected to a scanning line (not shown), and is givena predetermined timing. A power supply line DSL is connected to thedrain electrode of the drive transistor 1B.

In the above configuration of the pixel circuit, in the presentembodiment, the storage capacitor 1C and the auxiliary capacitor 1J arearranged adjacent to each other, and the wiring of the storage capacitor1C, which is brought into conduction with the gate electrode of thedrive transistor 1B, and the wiring of the auxiliary capacitor 1J, whichis brought into conduction with the cathode electrode of the organic ELelement 1D, are provided in different layers, which constitutes afeature.

Furthermore, in the present embodiment, in the above configuration ofthe pixel circuit, the wiring of the storage capacitor 1C, which isbrought into conduction with the source electrode of the drivetransistor 1B, and the wiring of the auxiliary capacitor 1J, which isbrought into conduction with the anode electrode of the organic ELelement 1D, are provided in different layers.

Therefore, since the wiring of the storage capacitor 1C, which isbrought into conduction with the gate electrode of the drive transistor1B, and the wiring of the auxiliary capacitor 1J, which is brought intoconduction with the cathode electrode of the organic EL element 1D, areprovided in different layers, the occurrence of a short between thewirings can be more effectively avoided as compared with the case wherethey are provided in the same layer.

Here, the above wirings are principal wirings that are disposed on aflat surface of a substrate and a flat surface on an insulating film onthe substrate, and contacts and the like provided between layers are notincluded. In the present embodiment, one of the above wirings is formedof a first metal wiring and the other is formed of polysilicon, which isformed with respect to the first metal wiring with a gate insulatingfilm therebetween.

System Configuration

FIG. 10 is a system configuration diagram showing an example of thepresent embodiment. As shown in FIG. 10, an organic EL display device100 is configured to include a pixel array unit 102 having pixels (PXLC)101 arranged in a two-dimensional matrix, and a driving unit arrangedaround the pixel array unit 102 to drive the pixels 101. The drivingunit for driving the pixels 101 includes, for example, a horizontaldrive circuit 103, a write scanning circuit 104, and a power supplyscanning circuit 105.

The pixel array unit 102 has scanning lines WSL-1 to WSL-m, power supplylines DSL-1 to DSL-m, and signal lines DTL-1 to DTL-n for the m-rown-column pixel array. The scanning lines WSL-1 to WSL-m and the powersupply lines DSL-1 to DSL-m are disposed for the individual rows, andthe signal lines DTL-1 to DTL-n are disposed for the individual pixelcolumns. The above configuration is the same as the system configurationshown in FIG. 1.

Wiring Structure

FIGS. 19A to 20 are diagrams illustrating an example wiring structureaccording to the present embodiment. FIG. 19A is a plan view, and FIGS.19B and 19C are cross-sectional views taken along the lines XIXB-XIXBand XIXC-XIXC of FIG. 19A, respectively. FIG. 20 is a cross-sectionalview taken along the line XX-XX of FIG. 19A. As in a pattern layoutshown in FIG. 19A, the storage capacitor 1C and the auxiliary capacitor1J are arranged so that, in terms of the area occupied thereby andpattern layout efficiency, at least one side of the storage capacitor 1Cand at least one side of the auxiliary capacitor 1J are adjacent to eachother.

The storage capacitor 1C is formed as a parallel flat plate having afirst electrode D1 and a polysilicon electrode p-Si serving as a secondelectrode, and the auxiliary capacitor 1J is formed as a parallel flatplate having a first electrode D1 and a polysilicon electrode p-Si′serving as a second electrode. In the present embodiment, therefore, thesecond electrodes of the storage capacitor 1C and the auxiliarycapacitor 1J are implemented by using separate polysilicon electrodesinstead of an integrated electrode.

Furthermore, the electrode of the storage capacitor 1C, which is broughtinto conduction with the gate g of the drive transistor 1B, and theelectrode of the auxiliary capacitor 1J, which is brought intoconduction with the cathode 1H of the organic EL element 1D, areprovided in different wiring layers. That is, one of the electrode ofthe storage capacitor 1C, which is brought into conduction with the gateg of the drive transistor 1B, and the electrode of the auxiliarycapacitor 1J, which is brought into conduction with the cathode 1H ofthe organic EL element 1D, is defined in the layer of a first metalwiring, and the other is defined in the layer of a polysilicon electrodep-Si.

FIGS. 19B and 19C show specific examples of wirings. In the figures, thenumerals in the parentheses correspond to the numerals of the electrodeshown in FIG. 9B.

First, in the specific example shown in FIG. 19B, the storage capacitor1C is configured such that the first electrode D1(g) serving as thefirst metal wiring is connected to the gate g of the drive transistor 1Band the polysilicon electrode p-Si(s) serving as the second electrode isconnected to the source s of the drive transistor 1B. The auxiliarycapacitor 1J is configured such that the first electrode D1(s) servingas the first metal wiring is connected to the source s of the drivetransistor 1B and the polysilicon electrode p-Si′ (1H) serving as thesecond electrode is connected to the cathode 1H of the organic ELelement 1D.

Accordingly, the electrode D1(g) of the storage capacitor 1C, which isbrought into conduction with the gate g of the drive transistor 1B, andthe electrode (polysilicon electrode p-Si′ (1H)) of the auxiliarycapacitor 1J, which is brought into conduction with the cathode 1H ofthe organic EL element 1D, are provided in different wiring layers.Since these wirings are not in the same layer, a structure in which ashort is less likely to occur due to dust or the like generated duringthe manufacturing process can be realized.

In the above wiring structure, furthermore, the second electrodes of thestorage capacitor 1C and the auxiliary capacitor 1J are also provided indifferent wiring layers. Since the layers are positioned with aninsulating layer diagonally held therebetween, the risk of a patternshort can be significantly reduced as compared with the case where thesecond electrodes are provided in the same layer.

Next, in the specific example shown in FIG. 19C, the storage capacitor1C is configured such that the first electrode D1(s) serving as thefirst metal wiring is connected to the source s of the drive transistor1B and the polysilicon electrode p-Si(g) serving as the second electrodeis connected to the gate g of the drive transistor 1B. The auxiliarycapacitor 1J is configured such that the first electrode D1(1H) servingas the first metal wiring is connected to the cathode 1H of the organicEL element 1D and the polysilicon electrode p-Si′(s) serving as thesecond electrode is connected to the source s of the drive transistor1B. In other words, the wiring structure shown in FIG. 19C has anopposite connection relationship to the connection relationship betweenthe wirings of the electrodes of the respective capacitors shown in FIG.19B.

Accordingly, the electrode D1(g) of the storage capacitor 1C, which isbrought into conduction with the gate g of the drive transistor 1B, andthe electrode (polysilicon electrode p-Si′ (1H)) of the auxiliarycapacitor 1J, which is brought into conduction with the cathode 1H ofthe organic EL element 1D, are provided in different wiring layers.Since these wirings are not in the same layer, a structure in which ashort is less likely to occur due to dust or the like generated duringthe manufacturing process can be realized.

In the above wiring structure, furthermore, the second electrodes of thestorage capacitor 1C and the auxiliary capacitor 1J are also provided indifferent wiring layers. Since the layers are positioned with aninsulating layer diagonally held therebetween, the risk of a patternshort can be significantly reduced as compared with the case where thesecond electrodes are provided in the same layer.

FIG. 20 is a cross-sectional view taken along the line XX-XX of FIG.19A. In FIG. 20, the wiring relationship between the electrodes shown inFIG. 19B is illustrated. As described earlier, the electrode(polysilicon electrode p-Si(s)) of the storage capacitor 1C, which isbrought into conduction with the source s of the drive transistor 1B,and the electrode D1(s) of the auxiliary capacitor 1J, which is broughtinto conduct with the anode of the organic EL element 1D (that is, thesource s of the drive transistor 1B), are provided in different wiringlayers. However, it is desirable that the respective electrodes bebrought into conduction with each other because the electrodes representthe same node.

Therefore, as shown in FIG. 20, a contact hole CH1 extending through theinterlayer insulating films M1 and M2 is connected to the electrodeD1(s) of the auxiliary capacitor 1J, and a contact hole CH2 extendingthrough the interlayer insulating film M2 is connected to the electrode(polysilicon electrode p-Si(s)) of the storage capacitor 1C. The contactholes CH1 and CH2 are brought into conduction with each other using asecond metal wiring D2.

A similar structure having an opposite connection relationship to theconnection relationship between the electrodes of the storage capacitor1C and the auxiliary capacitor 1J shown in FIG. 20 can be applied to thewiring relationship between the electrodes shown in FIG. 19C. DrivingMethod

FIG. 11 is a timing waveform diagram illustrating a method for driving adisplay device according to the present embodiment. The timing waveformdiagram shown in FIG. 11 is similar to the timing waveform diagram shownin FIG. 3 in that a light-emission period, threshold correction periods,and a sampling period & mobility correction period are repeated.

In the pixel layout (wiring structure) according to the presentembodiment described above, although the storage capacitor 1C and theauxiliary capacitor 1J are adjacent to each other, a short is lesslikely to occur between the gate g of the drive transistor 1B and thecathode 1H of the organic EL element 1D, thus reducing the occurrence ofa defective pixel. Therefore, the driving method described above isperformed to prevent the occurrence of a defective pixel incapable ofemitting light shown in FIG. 8 so that the potential of the video signalline DTL is not drawn to the cathode potential Vcath during the periods(F) to (J) shown in FIG. 8 or no pixels whose luminance increases aregenerated.

In the embodiment described above, the application to an organic ELdisplay device including organic EL elements as electro-optical elementsof the pixels 101 has been described by way of example. However,embodiments of the present invention are not limited to this applicationexample, and can be applied to any display device including acurrent-driven electro-optical element (light-emitting element) whoselight emission luminance changes in accordance with the current value ofa current flowing in the device.

Furthermore, the pixels 101 each having a 2Tr/1C pixel configurationincluding two transistors (Tr) and one capacitor (C) by way of example.However, embodiments of the present invention are not limited thereto,and can also be applied to any other pixel configuration such as a4Tr/1C pixel configuration including four transistors (Tr) and onecapacitor (C).

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Applications JP 2008-315467 filedin the Japan Patent Office on Dec. 11, 2008 and 2008-316551 filed in theJapan Patent Office on Dec. 12, 2008, the entire content of which ishereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A display device comprising: a pixel array unithaving pixels arranged in a matrix, at least one of the pixels having anelectro-optical element, a first capacitor, a second capacitor, a firsttransistor configured to supply a data signal to the first capacitor,and a second transistor configured to flow a drive current to theelectro-optical element; a data signal line extending in a firstdirection; and a scan line extending in a second direction differentfrom the first direction, wherein, the first capacitor has a firstwiring and a second wiring overlapped with the first wiring partly, thesecond capacitor has a third wiring and a fourth wiring overlapped withthe third wiring partly, the first wiring and the third wiring aredisposed and not connected each other in a first layer, the secondwiring and the fourth wiring are disposed and connected each other in asecond layer which is different from the first layer, a gate of thesecond transistor and the first wiring are connected each other in thefirst layer, and in a plan view, the first capacitor and the secondcapacitor are arranged in the second direction.